It is known to use various forms of collapsable and fold up ladders for both domestic and commercial use. A number of these prior art embodiments are very bulky when folded and are extremely difficult to carry. In addition several of these ladders require time consuming and difficult processes for dis-engaging the ladder after use. Correspondingly, most of these known ladders are troublesome to set up for use after storage.
Typical fold up ladders are disclosed in U.S. Pat. Nos. 3,216,526; 3,554,318; 3,655,012; 3,730,295; and 3,811,151.
At present, the fold up ladders known on the market consist of sections of several treads which are almost of the same length as that of the main strut of the portable ladder itself, to which it backs. These additional sections are linked by clamps to the couple of main struts between which the treads are placed.
These clamps secure the struts of the main and secondary sections allowing the longitudinal extension of this secondary section along the main one in the length it allows and its securing required by means of anchorage of one section in relation to the other. Another design consist in linking both sections, main and secondary on their ends by a hinged joint.
Nevertheless, this other solution is less reliable for the use of the ladder, as the securing lugged nut has to exert a great pressure in the aligned position in order to avoid the collapsing of the end of the ladder once it has been subject to the load of the person stepping on the additional top section, the effect of which load is still aggravated by the increase originated by the lever arm of the lengthening section itself. Therefore, this model is still less safer than the first. Nevertheless, both show the drawback of the difficulty of handling of collapsible ladders, as well as that of their weightiness and of that of requiring too much space when not in use, specially if they have to be carried from one working site to another, as they usually do not fit into small cars.
As noted above, the presently available ladders have serious drawbacks when assembling for use, or dis-engaging for storage. In addition they are relatively expensive to manufacture and not always structurally reliable when in use.